Printed circuit board, method of manufacturing the same and connection terminal

ABSTRACT

A read wiring trace and a write wiring trace are formed on an insulating layer. Connection terminals made of conductor are connected to the read wiring trace and the write wiring trace, respectively. Each connection terminal has at least one corner with a radius of curvature of not larger than 35 μm.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a printed circuit board, a method ofmanufacturing the same and a connection terminal.

(2) Description of Related Art

Actuators are used in drives such as hard disc drives. Such an actuatorincludes an arm provided rotatably around a rotation shaft, and asuspension board with a circuit for a magnetic head that is attached tothe arm. The suspension board with the circuit is a printed circuitboard for positioning the magnetic head at a desired track of a magneticdisc.

Signal lines and connection terminals are formed on the suspension boardwith the circuit. A head slider including the magnetic head is attachedon the connection terminals of the suspension board with the circuit.The magnetic head is electrically connected to another electroniccircuit through the connection terminals and the signal lines on thesuspension board with the circuit.

The connection terminals are manufactured by etching described below.(See, for example, JP 8-283966 A.) Resists are formed on both sides of ametal substrate. Then, a desired resist pattern is formed by selectiveexposure, development and drying, etc. Thereafter, part of the metalsubstrate that is exposed on the resist pattern is etched. Finally, theresist pattern is removed from the metal substrate after the completionof the etching, whereby a product with the desired pattern (connectionterminals in this example) is obtained.

BRIEF SUMMARY OF THE INVENTION

When rectangular connection terminals are formed by the etchingdescribed above, roundness is generated on the corners of the connectionterminals. In this case, the bonding areas of the connection terminalsare reduced when an electronic component such as a head slider and theconnection terminals are bonded to each other by a solder. In recentyears, printed circuit boards have been made finer, and thus, the bondstrength of the connection terminals and the other electronic componentsweakens since the bonding areas of the connection terminal are reduced.As a result, the connection reliability of the connection terminalsdeteriorates.

An object of the present invention is to provide a printed circuit boardhaving a connection terminal in which connection reliability can besecured and which can be made finer, a method of manufacturing theprinted circuit board, and such a connection terminal.

(1) According to an aspect of the present invention, a printed circuitboard includes an insulating layer, a wiring trace formed on theinsulating layer and a connection terminal made of conductor that iselectronically connected to the wiring trace, wherein the connectionterminal has at least one corner with a radius of curvature of notlarger than 35 μm.

In the printed circuit board, the connection terminal made of conductoris electronically connected to the wiring trace on the insulating layer.The radius of curvature of at least one corner of the connectionterminal is not larger than 35 μm. In this case, the corner is hardlyrounded. Therefore, the reduction of the bonding area due to theroundness of the corner can be suppressed. As a result, the connectionreliability of the connection terminal can be secured and the suspensionboard can be made finer.

(2) The conductor may include stainless steel and the radius ofcurvature of the at least one corner of the connection terminal may benot larger than 30 μm. In this case, the reduction of the bonding areaof the connection terminal including stainless steel can be moresufficiently suppressed.

(3) The conductor may include copper and the radius of curvature of theat least one corner of the connection terminal may be not larger than 10μm. In this case, the reduction of the bonding area of the connectionterminal including the copper can be more sufficiently suppressed.

(4) The connection terminal may have first and second sides parallel toeach other and a third side orthogonal to the first and second sides,and at least one corner includes a first corner that is formed by thefirst and third sides, and a second corner that is formed by the secondand third sides.

In this case, the first and second corners are hardly rounded.Therefore, the reduction of the bonding area of the connection terminalcan be further sufficiently suppressed.

(5) The width between the first and second sides may be not larger than70 μm. In this case, the suspension board can be sufficiently made finerwhile the reduction of the bonding area of the connection terminal issuppressed.

(6) The connection terminal may be configured to be electricallyconnectable to a magnetic head and transmittable of an electric signalbetween the magnetic head and an electronic circuit through the wiringtrace and the connection terminal.

In this case, the connection terminal and the magnetic head areelectrically connected and the electric signal is transmitted betweenthe magnetic head and the electronic circuit through the printed circuitboard. Because the reduction of the bonding area of the connectionterminal is suppressed, a weakening of bond strength of the connectionterminal and the magnetic head is suppressed. As a result, theconnection reliability between the connection terminal and the magnetichead can be improved.

(7) According to another aspect of the present invention, a method ofmanufacturing a printed circuit board includes the steps of forming aconductor trace that has a side extending in one direction on aninsulating layer, forming a first etching resist on the insulating layerthat has an edge crossing the side of the conductor trace and coverspart of the conductor trace, and forming a connection terminal that hasat least one corner by removing a portion of the conductor trace exposedon the first etching resist by etching.

In the method of manufacturing the printed circuit board, the conductortrace that has the side extending in one direction is formed on theinsulating layer. The first etching resist that has the edge crossingthe side of the conductor trace and covers part of the conductor traceis formed on the insulating layer. A portion of the conductor trace thatis exposed on the first etching resist is removed by etching. As aresult, the side that extends in another direction crossing the onedirection mentioned above is formed on the conductor trace, and theconnection terminal that has at least one corner is formed.

In this case, the corner is hardly rounded. Therefore, the reduction ofthe bonding area of the connection terminal due to the roundness of thecorner can be suppressed. As a result, the printed circuit board can bemade finer while the connection reliability of the connection terminalcan be secured.

(8) A radius of curvature of the at least one corner of the connectionterminal may be not larger than 35 μm. In this case, the reduction ofthe bonding area of the connection terminal due to the roundness of thecorner can be suppressed. As a result, the printed circuit board can bemade finer while the connection reliability of the connection terminalcan be secured.

(9) The step of forming the conductor trace may include the steps offorming a second etching resist on the insulating layer that has an edgeextending in the one direction to cover part of a conductor layer formedon the insulating layer, and forming the conductor trace by removing aportion of the conductor layer exposed on the second etching resist byetching.

In this case, the conductor trace that has the side extending in the onedirection is formed by etching the conductor layer using the secondetching resist, and the connection terminal that has at least one corneris formed by etching the conductor trace using the first etching resist.Thus, the connection terminal with hardly any roundness on its cornercan easily be formed by two-time etching.

(10) The step of forming the conductor trace may include the step offorming the conductor trace that has the first and second sides parallelto each other, and the step of forming the first etching resist on theinsulating layer may include the step of forming the first etchingresist on the insulating layer that has an edge orthogonal to the firstand second sides, the step of forming the connection terminal that hasthe at least one corner may include the step of forming the connectionterminal that has a third side orthogonal to the first and second sidesby removing a portion of the conductor trace exposed on the firstetching resist by etching, and the at least one corner of the connectionterminal may include a first corner formed by the first and third sides,and a second corner formed by the second and third sides.

In this case, the print circuit board that includes the connectionterminal having the first and second corners is manufactured. The firstand second corners of the connection terminal are hardly rounded.Therefore, the reduction of the bonding area of the connection terminalcan be further sufficiently suppressed.

(11) According to a further aspect of the present invention, aconnection terminal that is to be electrically connected to a wiringtrace to transmit the electrical signal, comprising at least one cornerhaving a radius of curvature of not larger than 35 μm.

In this connection terminal, the radius of curvature of at least onecorner is not larger than 35 μm. In this case, the corner is hardlyrounded. Therefore, the reduction of the bonding area of the connectionterminal can be suppressed. As a result, the connection terminal can bemade finer while the connection reliability of the connection terminalcan be secured.

According to the present invention, it is possible to make the printedcircuit board finer while securing the connection reliability of theconnection terminal.

Other features, elements, characteristics, and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments of the present invention with reference to theattached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a top view of a suspension board according to a firstembodiment of the present invention;

FIGS. 2 (a) and 2 (b) are cross-sectional views of the suspension boardillustrated in FIG. 1;

FIGS. 3 (a) to 3(c) are diagrams showing the steps of manufacturing thesuspension board illustrated in FIG. 1;

FIGS. 4 (a) to 4(d) are diagrams showing the steps of manufacturing thesuspension board illustrated in FIG. 1;

FIGS. 5 (a) to 5(c) are diagrams showing the steps of manufacturing thesuspension board illustrated in FIG. 1;

FIG. 6 is an enlarged bottom view showing a tongue of a suspension boardand its periphery;

FIGS. 7 (a) to 7(c) are diagrams showing the steps of manufacturing asuspension board according to a second embodiment;

FIG. 8 is a bottom view showing one step of manufacturing a suspensionboard according to a third embodiment; and

FIGS. 9 (a) and 9(b) are bottom views showing one step of manufacturinga suspension board according to a fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] First Embodiment

A printed circuit board with connection terminals according to the firstembodiment of the present invention and a method of manufacturing thesame will be described below with reference to the drawings. Asuspension board used for an actuator in a hard disc drive as theprinted circuit board according to the first embodiment of the presentinvention will be described below.

(1) Configuration of Suspension Board

FIG. 1 is a top view of the suspension board according to the firstembodiment of the present invention. As shown in FIG. 1, a suspensionboard 1 includes a suspension body 100 formed of a metallic and elongatesupport substrate. Write wiring traces W1 and W2 and read wiring tracesR1 and R2, as shown by thick dotted lines, are formed on the suspensionbody 100. The write wiring trace W1 and the write wiring trace W2constitute a signal line pair. The read wiring trace R1 and the readwiring trace R2 constitute a signal line pair.

At one end of the suspension body 100, a magnetic head supportingportion (hereinafter referred to as a tongue) 12 is provided by forminga U-shaped opening 11. The tongue 12 is bent along a broken line R toform a predetermined angle with respect to the suspension body 100. Onthe lower surface of the tongue 12 at one end of the suspension body100, four connection terminals 21, 22, 23 and 24 are formed. A headslider that includes a magnetic head is attached to the connectionterminals 21 to 24 on the lower surface of the tongue 12.

In the present embodiment, each of the connection terminals 21 to 24 hasa rectangular shape. The width of each of the connection terminals 21 to24 (the width between sides L1 and L2 of FIG. 6, described later) ispreferably not larger than 70 μm. In this case, the suspension board 1can be made finer and smaller.

Four connection terminals 31, 32, 33 and 34 are formed on the uppersurface of the other end of the suspension body 100. An electroniccircuit such as a preamplifier is connected to the connection terminals31 to 34. The connection terminals 21 to 24 of the tongue 12 and theconnection terminals 31 to 34 of the other end of the suspension body100 are electrically connected by the write wiring traces W1 and W2 andthe read wiring traces R1 and R2, respectively. Further, a plurality ofholes H are formed in the suspension body 100.

The suspension board 1 is provided in a hard disc device. An electriccurrent flows through the pair of the write wiring traces W1 and W2 atthe time of writing information into a magnetic disc. Further, theelectric current flows through the pair of the read wiring traces R1 andR2 at the time of reading information from the magnetic disc.

Next, the connection terminals 21 to 24 of the suspension board 1 andits peripheral portions will be described in detail below. FIG. 2 is across-sectional view of the suspension board 1 of FIG. 1. FIG. 2 (a)shows a cross sectional view taken along the line A-A of the suspensionboard 1 of FIG. 1, and FIG. 2 (b) shows a cross sectional view takenalong the line B-B of the suspension board 1 of FIG. 1.

As shown in FIG. 2 (a), an insulating layer 41 made of polyimide, forexample, is formed on a metallic support substrate 10 made of stainlesssteel, for example. The write wiring traces W1 and W2 and the readwiring traces R1 and R2 are spaced apart from and parallel to each otheron the insulating layer 41. The write wiring traces W1 and W2 extendalong one lateral side of the insulating layer 41 and the read wiringtraces R1 and R2 extend along the other lateral side of the insulatinglayer 41. A cover layer 43 made of polyimide, for example, is formed onthe insulating layer 41 to cover the write wiring traces W1 and W2 andthe read wiring traces R1 and R2.

The write wiring traces W1 and W2 and the read wiring traces R1 and R2that extend along the one lateral side and the other lateral side of theinsulating layer 41 bend inward at one end of the suspension body 100 ofFIG. 1, and bend towards the tongue 12, and then extend to the tongue 12as shown in FIG. 2 (b). The write wiring traces W1 and W2 and the readwiring traces R1 and R2 on the tongue 12 are respectively connected tothe connection terminals 21 to 24 on the lower surface of the tongue 12.

(2) Method of Manufacturing the Suspension Board

A method of manufacturing the suspension board 1 of FIG. 1 will bedescribed below. FIGS. 3 to 5 are schematic diagrams showing the stepsof manufacturing the suspension board 1 of FIG. 1. In FIGS. 3 (a) to 3(c), cross sectional views taken along the line B-B of the suspensionboard 1 are shown in the left and top views of the tongue 12 of thesuspension board 1 of FIG. 1 and its periphery are shown in the right.In FIGS. 4 (a) to 5 (c), cross sectional views taken along the line B-Bof the suspension board 1 of FIG. 1 are shown in the left and bottomviews of the tongue 12 and its periphery of the suspension board 1 ofFIG. 1 are shown in the right. The same hatched and dotted patternsapplied to the members of the cross sectional views are applied to themembers of the top view of FIGS. 3 (a) to 3 (c) and the bottom views ofFIGS. 4 and 5 in order to facilitate understanding of the configuration.

First, as shown in FIG. 3 (a), the insulating layer 41 made of polyimideis formed on the support substrate 10 made of stainless steel. Thethickness of the support substrate 10 is not less than 10 μm nor morethan 50 μm, for example. The thickness of the insulating layer 41 is notless than 5 μm nor more than 15 μm, for example. Here, the insulatinglayer 41 is formed in the same shape as the suspension board 1 ofFIG. 1. Further, a plurality of openings 41 h (four in the exampleillustrated in FIG. 3 (a)) are formed in the insulating layer 41. As aresult, part of the support substrate 10 is exposed in the openings 41h.

Then, as shown in FIG. 3 (b), the write wiring traces W1 and W2 and theread wiring traces R1 and R2 having predetermined patterns are formed onthe insulating layer 41 and the support substrate 10 exposed in theopenings 41 h. The thickness of each of the write wiring traces W1 andW2 and the read wiring traces R1 and R2 is not less than 6 μm nor morethan 18 μm, for example. Further, each of the width of the write wiringtraces W1 and W2 and the read wiring traces R1 and R2 is not less than 8μm nor more than 50 μm, for example. Moreover, each of the spacingbetween the write wiring traces W1 and W2 and the spacing between theread wiring traces R1 and R2 is not less than 8 μm nor more than 100 μm,for example.

Next, as shown in FIG. 3 (c), a cover layer 43 made of polyimide isformed on the insulating layer 41 to cover the write wiring traces W1and W2 and the read wiring traces R1 and R2. The thickness of the coverlayer 43 is not less than 2 μm nor more than 10 μm, for example.

Then, as shown in FIG. 4 (a), a resist film 18 is formed using aphotosensitive dry film resist, for example, on the lower surface of thesupport substrate 10. Next, as shown in FIG. 4 (b), the resist film 18is exposed in a predetermined pattern, and then developed by using adevelopment liquid such as sodium carbonate whereby an etching resist 18a is formed. Here, the etching resist 18 a has a plurality of (four inthe example illustrated in FIG. 4 (b)) rectangular insular parts IR in arectangular opening OP. Each insular part IR has edges 18 b extending inone direction.

Thereafter, as shown in FIG. 4 (c), the support substrate 10 is etchedusing ferric chloride solution and cupric chloride solution as etchingsolution, whereby a plurality of conductor traces 10 a, 10 b, 10 c and10 d (four in the example illustrated in FIG. 4 (c)) made of stainlesssteel are formed on the lower surface of the insulating layer 41. Theconductor traces 10 a to 10 d are electrically connected to the writewiring traces W1 and W2 and the read wiring traces R1 and R2,respectively, and separated from one another.

Each of conductor traces 10 a to 10 d has a substantially rectangularshape. The four corners of each insular part IR of the etching resist 18a are slightly rounded and the etching solution penetrates beneath thefour corners of the etching resist 18 a. Therefore, it is difficult toform each corner of the conductor traces 10 a to 10 d so as to have aradius of curvature of not larger than 35 μm.

Then, after removing the etching resist 18 a, as shown in FIG. 4 (d), aresist film 19 is formed using the photosensitive dry film resist, forexample, on the lower surfaces of the conductor traces 10 a to 10 d andthe support substrate 10. Next, as shown in FIG. 5 (a), the resist film19 is exposed in a predetermined pattern, and then developed using thedevelopment liquid such as sodium carbonate, whereby the etching resist19 a is formed.

Here, the etching resist 19 a has a rectangular opening OP1 thatincludes the corners on one end of each of the conductor traces 10 a to10 d, and a rectangular opening OP2 that includes the corners on theother end of each of the conductor traces 10 a to 10 d. One side of eachof the openings OP1 and OP2 crosses (i.e., in the example of FIG. 5 (a),is orthogonal to) each of the lateral sides of the conductor traces 10 ato 10 d. This causes both ends of the conductor traces 10 a to 10 d in alongitudinal direction to be exposed on the etching resist 19 a.Further, the other part of the etching resist 19 a is formed in the sameshape as the suspension board 1 of FIG. 1.

Next, the conductor traces 10 a to 10 d and the support substrate 10 areetched using the ferric chloride solution and the cupric chloridesolution as the etching solution. Here, as shown in FIG. 5 (b), bothends in the longitudinal direction of the conductor traces 10 a to 10 dare removed. Thereafter, as shown in FIG. 5 (c), the etching resist 19 ais removed and then the rectangular connection terminals 21 to 24 areformed. As a result, the suspension board 1 is completed.

In this case, in the step illustrated in FIG. 5 (b), the linear edges 19b of the openings OP1 and OP2 are orthogonal to the lateral sides of theconductor traces 10 a to 10 d. Further, the etching solution penetratesalong the linear edges 19 b of the openings OP1 and OP2 of the etchingresist 19 a. Therefore, the radius of curvature of each corner of theconnection terminals 21 to 24 can be not larger than 35 μm. When theconnection terminals 21 to 24 are made of stainless steel, the radius ofcurvature of each corner of each of the connection terminals 21 to 24 ispreferably not larger than 30 μm and more preferably 0 μm.

(3) Effect

FIG. 6 is an enlarged bottom view showing the tongue 12 of thesuspension board 1 and its periphery. Because the insular parts IR ofthe etching resist 18 a of FIG. 4 (b) have the edges 18 b arranged inone direction, each of the connection terminals 21 to 24 has two sidesL1 and L2 parallel to each other as shown in FIG. 6. Further, becausethe openings OP1 and OP2 of the etching resist 19 a of FIG. 5 (a) havethe edges 19 b extending in the direction orthogonal to the onedirection, each of the connection terminals 21 to 24 has two sides L3and L4 orthogonal to the sides L1 and L2 as shown in FIG. 6.

A corner A1 is formed between the sides L1 and L3, a corner A2 is formedbetween the sides L2 and L3, a corner A3 is formed between the sides L1and L4, and a corner A4 is formed between the sides L2 and L4. Theradius of curvature of each corner A1 to A4 is formed to be not largerthan 35 μm. That is, each corner A1 to A4 is hardly rounded. Therefore,the reduction of the bonding area of the connection terminals 21 to 24due to the roundness of the corners A1 to A4 can be suppressed. As aresult, this enables the suspension board 1 to be made finer whilesecuring the connection reliability of the connection terminals 21 to24.

Furthermore, as can be understood from other embodiments describedlater, because the radius of curvature of the corners A1 to A4 isreduced, the maximum plastic strain of the connection terminals 21 to 24becomes smaller when stress is applied to the connection terminals 21 to24.

[2] Second Embodiment

While the connection terminals 21 to 24 are formed to have the radius ofcurvature of not larger than 35 μm in the first embodiment, theinvention is not limited to this. The connection terminals 21 to 24 maybe formed such that the radius of curvature of part of the corners isnot larger than 35 μm.

FIG. 7 is a schematic diagram showing the steps of manufacturing thesuspension board according to the second embodiment. The method ofmanufacturing suspension board 1 according to the present embodiment hasthe steps similar to those of the method of manufacturing the suspensionboard 1 illustrated in FIGS. 3 (a) to 4 (d) according to the firstembodiment. Description will be made of the method of manufacturing thesuspension board 1 according to the present embodiment by referring todifferences from the method of manufacturing the suspension board 1according to the first embodiment will be described.

Following the step illustrated in FIG. 4 (d), as shown in FIG. 7 (a),the etching resist 19 a having a predetermined pattern is formed byprocessing the resist film 19. Here, the etching resist 19 a has therectangular opening OP2 that includes the corners on one end of each ofthe conductor traces 10 a to 10 d. The edges 19 b of the opening OP2cross (i.e., in the example of FIG. 7 (a), is orthogonal to) each of thelateral side of the conductor traces 10 a to 10 d. This causes one endsof the conductor traces 10 a to 10 d in the longitudinal direction to beexposed on the etching resist 19 a.

Then, the conductor traces 10 a to 10 d and the support substrate 10 areetched. Here, as shown in FIG. 7 (b), one ends of the conductor traces10 a to 10 d in the longitudinal direction are removed. Thereafter, theetching resist 19 a is removed, thereby forming the rectangularconnection terminals 21 to 24, as shown in FIG. 7 (c). As a result, thesuspension board 1 is completed. In this case, the radius of curvatureof the corners on the one end side of each of the connection terminals21 to 24 (the corners A1 and A2 of FIG. 6) can be made to be not largerthan 35 μm.

[3] Third Embodiment

While in the step illustrated in FIG. 4 (b) according to the firstembodiment, the insular parts IR are formed in a rectangular shape, theinvention is not limited to this. The insular parts IR may be formed inanother shape that has the edges 18 b extending in one direction. FIG. 8is a bottom view showing the method of manufacturing the suspensionboard according to the third embodiment.

In the present embodiment, instead of the step illustrated in FIG. 4 (b)in the first embodiment, the etching resist 18 a that has a plurality of(four in the example illustrated in FIG. 8) insular parts IR in therectangular opening OP is formed as shown in FIG. 8. Here, the insularparts IR have the edges 18 b extending in the one direction, and bothends of the insular parts IR in a longitudinal direction havesemicircular shape. As a result, in the step illustrated in FIG. 4 (c),the conductor traces 10 a to 10 d with both ends having the semicircularshape in the longitudinal direction are formed.

Thereafter, similarly to the steps illustrated in FIGS. 4 (d) to 5 (c),both ends of the conductor traces 10 a to 10 d in the longitudinaldirection are removed, thereby forming the rectangular connectionterminals 21 to 24 that have the corners with their radius of curvatureof not larger than 35 μm.

[4] Fourth Embodiment

While in the step illustrated in FIG. 5 (a) in the first embodiment, theedges 19 b of the etching resist 19 a are formed to be orthogonal toeach lateral side of each of the conductor traces 10 a to 10 d, theinvention is not limited to this. FIG. 9 is a bottom view showing onestep of manufacturing the suspension board according to the fourthembodiment.

In the present embodiment, as shown in FIG. 9 (a), the edges 19 b of theetching resist 19 a are formed to cross each of the lateral sides of theconductor traces 10 a to 10 d at a desired angle different from a rightangle. In this case, both ends of the conductor traces 10 a to 10 d inthe longitudinal direction are removed and then the etching resist 19 ais removed, so that the connection terminals 21 to 24 with an arbitraryquadrangle can be formed as shown in FIG. 9 (b).

[5] Other Embodiments

(1) While in the above-mentioned embodiment, the connection terminals 21to 24 are made of stainless steel, the invention is not limited to this.The connection terminals 21 to 24 may be made of another metal such ascopper, gold (Au), silver or aluminum, or alloy such as copper alloy,gold alloy, silver alloy or aluminum alloy. When the connectionterminals 21 to 24 are made of copper, the radius of curvature of eachcorner of each of the connection terminals 21 to 24 is preferably 15 μm,and more preferably not larger than 10 μm and still more preferably 0μm.

(2) While in the above-mentioned embodiment, all of the connectionterminals 21 to 24 are formed to have the corners with the radius ofcurvature of not larger than 35 μm, the invention is not limited tothis. Part of the connection terminals 21 to 24 may be formed to havethe corners with a radius of curvature of not larger than 35 μm.

(3) While in the above-mentioned embodiment, the conductor traces 10 ato 10 d are formed by etching using the etching resist 18 a, theinvention is not limited to this. The conductor traces 10 a to 10 d maybe formed by other methods such as a semi-additive method or the like.

(4) While in the above-mentioned embodiment, the connection terminals 21to 24 are formed on the lower surface of the suspension board 1, theinvention is not limited to this. The connection terminals 21 to 24 maybe formed on the upper surface of the suspension board 1.

(5) In the suspension board 1 of FIG. 1, part or all of the connectionterminals 31 to 34 may be manufactured similarly to the method ofmanufacturing the connection terminals 21 to 24 in the first to fourthembodiments. Further, the connection terminals 31 to 34 may be formed onthe lower or upper surface of the suspension board 1.

[6] Correspondences between Elements in the Claims and Parts inEmbodiments

In the following paragraphs, non-limiting examples of correspondencesbetween various elements recited in the claims below and those describedabove with respect to various preferred embodiments of the presentinvention are explained.

The insulating layer 41 is an example of an insulating layer, the readwiring traces R1 and R2 or the write wiring traces W1 and W2 areexamples of a wiring trace, the connection terminals 21 to 24 areexamples of a connection terminal, the corners A1 to A4 are examples ofa corner, the suspension board 1 is an example of a printed circuitboard, the sides L1 to L3 are examples of first to third sidesrespectively, the corners A1 and A2 are examples of first and secondcorners respectively, and the etching resists 19 a and 18 a are examplesof first and second etching resists respectively.

As each of various elements recited in the claims, various otherelements having configurations or functions described in the claims canbe also used.

[7] Inventive Examples

In inventive examples 1 to 4 and a comparative example 1 describedbelow, the maximum plastic strain was evaluated by simulation afterstress was applied to a plurality of connection terminals with thecorners that were made of stainless steel and had different radii ofcurvature. The results are shown in Table 1. Here, the connectionterminals according to the inventive examples 1 to 4 and the comparativeexample 1 had a 50 μm-wide squareshape. Further, the radii of curvatureof the corners of the connection terminals according to the inventiveexamples 1 to 4 and the comparative example 1 were respectively 0 μm, 10μm, 20 μm, 30 μm and 50 μm.

TABLE 1 RADIUS OF MAXIMUM CURVATURE OF PLASTIC CORNER STRAIN INVENTIVE 0 μm 0.0092 EXAMPLE 1 INVENTIVE 10 μm 0.0093 EXAMPLE 2 INVENTIVE 20 μm0.0093 EXAMPLE 3 INVENTIVE 30 μm 0.0124 EXAMPLE 4 COMPARATIVE 50 μm0.0163 EXAMPLE 1

As shown in Table 1, the maximum plastic strains of the connectionterminals according to the inventive examples 1 to 3 were respectively0.0092, 0.0093 and 0.0093. Further, the maximum plastic strain of theconnection terminals according to the inventive example 4 was 0.0124. Onthe other hand, the maximum plastic strain of the connection terminalsaccording to the comparative example 1 was 0.0163.

From the results in the inventive examples 1 to 4 and the comparativeexample 1, it was confirmed that when the connection terminals were madeof stainless steel and had a 50 μm-wide squareshape, the increase in themaximum plastic strain was suppressed by setting the radius of curvatureof the corners to be not larger than 30 μm. In particular, it wasconfirmed that the increase in the maximum plastic strain was largelysuppressed by setting the radius of curvature of the corners to be notlarger than 20 μm.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1-6. (canceled)
 7. A method of manufacturing a printed circuit board,comprising the steps of: forming a conductor trace that has a sideextending in one direction on an insulating layer; forming on saidinsulating layer a first etching resist that has an edge crossing saidside of said conductor trace and covers part of said conductor trace;and forming a connection terminal that has at least one corner byremoving a portion of said conductor trace exposed on said first etchingresist by etching.
 8. The method of manufacturing the printed circuitboard according to claim 7, wherein a radius of curvature of said atleast one corner of said connection terminal is not larger than 35 μm.9. The method of manufacturing the printed circuit board according toclaim 7, wherein the step of forming said conductor trace includes thesteps of forming a second etching resist on said insulating layer thathas an edge extending in said one direction to cover part of a conductorlayer formed on said insulating layer, and forming said conductor traceby removing a portion of said conductor layer exposed on said secondetching resist by etching.
 10. The method of manufacturing the printedcircuit board according to claim 7, wherein the step of forming saidconductor trace includes the step of forming the conductor trace thathas first and second sides parallel to each other, the step of formingsaid first etching resist on said insulating layer includes the step offorming the first etching resist on said insulating layer that has anedge orthogonal to said first and second sides, the step of forming theconnection terminal that has said at least one corner includes the stepof forming said connection terminal that has a third side orthogonal tosaid first and second sides by removing a portion of said conductortrace exposed on said first etching resist by etching, and said at leastone corner of said connection terminal includes a first corner formed bysaid first and third sides, and a second corner formed by said secondand third sides.
 11. (canceled)